1. Field of the Invention
The present invention relates to integral-type dielectric duplexers using dielectric blocks, which are provided in mobile communication devices, and to communication apparatuses which include the same.
2. Description of the Related Art
Referring to FIG. 11, the structure of a known dielectric duplexer will now be described.
A substantially-rectangular-parallelepiped-shaped dielectric block 1 includes a plurality of plated through holes 2a to 2f containing inner conductors 3a to 3f, respectively. The inner conductors on the plated through holes define respective resonant cavities. An outer conductor 4 is formed on substantially the entire exterior surface of the dielectric block 1. In the vicinity of first ends of the plated through holes 2a to 2f (the right back side of the plated through holes as viewed in FIG. 11), inner-conductorless portions 33a to 33f are provided, thus forming open ends of the resonant cavities. Second ends (the left front side as viewed in FIG. 11) of the plated through holes are short-circuit ends which are directly coupled to the outer conductor 4. The face of the dielectric block located adjacent the short-circuit ends of the resonant cavities will be referred to as the short-circuit end face of the duplexer. In accordance with this structure a plurality of dielectric resonators are formed.
An input/output terminal 5 extends from a right side face of the dielectric block to a mounting surface (the bottom face in FIG. 11) of the dielectric block 1 which is opposed to a mounting board. The input/output terminal 5 is separated from the outer conductor 4 by an outer-conductorless portion 6 located therebetween. Although not shown in FIG. 11, a second input/output terminal is preferably formed extending from a left side face (opposite the right side face) to the bottom mounting surfaces. An antenna terminal 7 is formed between the plated through holes 2c and 2d and is separated from the outer conductor 4 by an outer-conductorless portion 8. The antenna terminal 7 extends from the short-circuit end face to the mounting surface. An antenna excitation hole 9 is formed as a through-hole in the same axial direction as that of the plated through holes 2a to 2f in the dielectric block 1. An electrode is formed on the inner surface of the antenna excitation hole 9 and is electronically coupled to the antenna terminal 7.
A first portion of the duplexer containing plated through holes 2a to 2c and a second portion of the duplexer containing the inner-conductor-formed holes 2d to 2f each function as a three-stage dielectric filer in which the resonant cavities formed by the inner conductors of the plated through holes are coupled to one another. The first portion is typically regarded as a transmitter filter and the second portion is typically regarded as a receiver filter.
The above-described known dielectric duplexer has the following problems.
FIG. 12 illustrates an enlarged section of the duplexer of FIG. 11 showing the distribution of ground current on a portion of the short-circuit end face thereof.
FIG. 12 shows the plated through holes 2d and 2e, the inner conductors 3d and 3e, the outer conductor 4, the antenna terminal 7, the outer-conductorless portion 8, the antenna excitation hole 9, a top electrode 10, which is part of the outer conductor, and a bottom electrode 11, which is also part of the outer conductor.
In response to a signal input to the dielectric duplexer, current flows from the inner electrodes to the outer conductor, which acts as a ground electrode. As shown in FIG. 12 the current flowing from the inner conductor 3e to the top electrode 10 is substantially equal to the current flowing from the inner conductor 3e to the bottom mounting electrode 11. As a result, there is substantially no potential difference between the top electrode 10 and the bottom electrode 11 in the area of the plated through hole 2e, and a TE (transverse electric) mode having an electric field component perpendicular to the top electrode 10 and the bottom electrode 11 is not excited.
In contrast, such a mode is excited in the area of the plated through hole 2d because of the presence of the outer-conductorless portion 8 which is provided on the short-circuit end face and the bottom mounting surface of the dielectric block, but not on the top surface thereof A current flowing from the inner conductor 3d adjacent to the antenna terminal 7 to the top electrode 10 is greater than a current flowing from the inner conductor 3d to the bottom electrode 11. Thus, a potential difference is generated between the top electrode 10 and the bottom electrode 11, and hence an electric field is generated. Accordingly, the TE mode having an electric field component perpendicular to the top electrode 10 and the bottom electrode 11 is excited.
Generally in a duplexer, the attenuation band of a transmitter filter is the pass band of a receiver filter, and the attenuation band of the receiver filter is the pass band of the transmitter filter. When a resonator forming the receiver filter, particularly a resonator adjacent to an antenna excitation hole, excites a TE mode in the pass band of the receiver filter, part of a transmission signal passing through the transmitter filter couples with the resonator forming the receiver filter, and the coupled signal is transmitted to the antenna excitation hole. Thus, the attenuation characteristic of the transmitter filter deteriorates significantly. In contrast, when a resonator forming the transmitter filter, particularly a resonator adjacent to the antenna excitation hole, excites the TE mode in the pass band of the transmitter filter, the attenuation characteristic of the receiver filter deteriorates significantly.
When a wave in a TE mode propagates between the transmitter filter and the receiver filter, the attenuation characteristics deteriorate.
Accordingly, it is an object of the present invention to provide a dielectric duplexer which has a simple structure having improved attenuation characteristics by reducing the excitation of undesirable modes in which a wave propagates between filters and to provide a communication apparatus using the same.
According to an aspect of the present invention, a dielectric duplexer comprises:
a dielectric block having an outer surface including top, bottom, front and rear surfaces;
a plurality of plated through holes extending through the dielectric block between the front to the rear surfaces thereof, each of the plated through holes having a respective inner conductor formed on an inner surface thereof;
an antenna excitation hole extending through the dielectric block from the front to the rear surface thereof, the antenna excitation hole having an electrode formed on an inner surface thereof;
an outer conductor located on the outer surface of the dielectric block and being directly connected to the inner conductors at the front surface of the dielectric block;
input/output terminals located on the outer surface of the dielectric block and being spaced from the outer conductor;
an antenna terminal located on the front surface and being directly coupled to the antenna excitation hole electrode, the antenna terminal being separated from the outer conductor by a conductorless area extending from the front to the bottom surfaces of the dielectric block; and
means for adjusting the relative flow of current through the outer conductor between the inner electrode of a first one of the plated through holes which is located adjacent the antenna terminal and the upper and lower surfaces of the dielectric block so as to cause the two current flows to be substantially equal.
The adjusting means may include at least one electrodeless portion formed on the outer conductor located on the front face of the dielectric block and located adjacent the antenna excitation hole. The embodiment makes it possible to tune the duplexer by removing portions of the outer conductor.
The adjusting means may alternatively be a portion of the first plated through hole which terminates at the front surface of the dielectric block and is located closer to the bottom surface than the top surface. The first plated through hole can have a single central axis or can be offset with two parallel but spaced central axes. Accordingly, when a mold is set in advance so as to obtain the desired characteristics, a dielectric duplexer having improved attenuation characteristics can be easily formed without processing the outer shape of the dielectric duplexer.
The adjusting means can also be an indentation formed in the front surface of the dielectric block so as to adjust the relative flow of current between the inner conductor of the first plated through hole and the top and bottom surfaces of the dielectric block. In the preferred embodiment, the indentation comprises a planar surface extended, at an oblique angle to the top and bottom surfaces of the dielectric block. In accordance with this embodiment, a dielectric duplexer can be easily formed without using a plated through hole having a complicated shape.
According to another aspect of the present invention, a communication apparatus including the foregoing dielectric duplexer is provided. Accordingly, a communication apparatus having improved communication characteristics can be easily formed.